Integrated circuit ("IC") chips contain a variety of miniaturized electronic circuitry and are widely used on printed circuit boards manufactured by the electronics industry to form composite electrical circuits. A typical IC chip or die is located within a ceramic substrate and is the actual electronic circuitry that is coupled to leads that extend to contacts or terminals positioned about the perimeter of the substrate or in various patterns across the bottom surface such as land grid arrays. This assembly is referred to as an IC package or a chip carrier. During operation of the electronic circuitry, the die generates heat and this heat can destroy the active elements in the die. In addition, heat can severely limit the speed and power capabilities of the circuitry of an IC chip. Therefore, it is necessary to dissipate the heat generated by the die in the IC chip.
One means of dissipating the heat generated by the IC chip is the use of a heat sink. For example, the heat sink or radiating member can be integrated into the top of the IC package to radiate heat from the top of the IC package, as shown in Spaight U.S. Pat. No. 4,092,697, Sugimoto et al. U.S. Pat. No. 4,803,546, and Werther U.S. Pat. No. 4,750,092. In another example of heat dissipation, thermal conducting elements are used to transmit heat to a heat sink which is mounted on a printed circuit ("PC") board on the side which is opposite to the IC package, as shown in Pitasi U.S. Pat. No. 4,682,269 and IBM Technical Disclosure Bulletin Vol. 13 No. 1, June 1970 at page 58. In yet another example of heat dissipation, a removable heat sink is attached to the upper surface of an IC package, as shown in Bright et al. U.S. Pat. No. 4,716,494.
These methods could be used with IC packages which direct the thermal flow upward, i.e., away from the PC board. In these IC packages, the thermal transfer and the electrical contacts are located on opposing surfaces of the IC package. These IC packages use a "cavity down" configuration and incorporate a copper/tungsten slug into the cavity. The die is mounted directly onto the copper/tungsten slug and a silver glass paste is used to attach the die to the slug in order to minimize voiding. The die and slug are attached to the upper portion of the IC package. The heat generated by the die is conducted to the slug which then dissipates the heat to the air above and surrounding the IC package. Thus, these IC packages direct the thermal flow upward, i.e., away from the PC board or socket.
However, these prior art heat sinking methods are not suitable for IC packages which direct the thermal flow downward, i.e., toward the PC board or into the socket. In these IC packages, the thermal transfer area and electrical contacts are located on the same surface. These IC packages use a "cavity up" configuration and also incorporate a metal slug into the cavity to dissipate the heat from the die. However, in the cavity up configuration, the metal slug is attached to the lower portion of the IC package, i.e., the mounting side of the IC package. In addition, the metal slug can incorporate posts or a plate. The ceramic substrate, which forms the exterior of the IC package, is molded around the posts or plate so that the ends of the posts or the bottom surface of the plate protrude through the ceramic material to form thermal lands or pads. Consequently, in the cavity up configuration, the thermal flow is directed downward, i.e., toward the PC board or into the socket.
This cavity up configuration permits a higher density of inputs and outputs ("I/O") to the die and also reduces the length of the traces which connect the I/O's on the die to the pads or lands on the bottom of the IC package. The shorter traces result in faster signal speeds since the signal travels a shorter distance along the trace.
Furthermore, other methods for dissipating heat from IC packages which use a cavity up configuration have disadvantages. For example, if the thermal path between the IC package and the PC board is completed by soldering, the heat transfer is compromised because solder is a poor thermal coupler. In addition, solder joints are less reliable in a large array area captured under the IC package and soldering would increase the manufacturing costs. Another alternative would be to use a heat sink which penetrates the PC board. However, such a heat sink would require relatively large thru-holes in the PC board and these thru-holes would waste vast areas of precious electrical real estate on the PC board.
Another alternative would be heat dissipation via a copper layer or layers on or embedded in the PC board. However, these copper layers are very thin which greatly reduces the thermal conduction. Another alternative would be heat dissipation via the low expansion planes. The low expansion planes are incorporated into multilayer PC boards to control the thermal expansion of the PC board. Conventional multilayer boards use copper-clad Invar as a low expansion plane. However, low expansion planes are expensive and would increase the manufacturing cost. In addition, the low expansion planes eliminate areas where traces can be used on the PC board and results in wasted areas of potential electrical real estate. Therefore, a new means to dissipate heat from an electrical component was necessary.
Furthermore, IC packages are either soldered to the PC board or mounted into sockets or socket cavities which are attached to the PC board. The sockets are electrically attached to the PC board at the position designated for the IC package. The IC package is then inserted into the IC socket or socket cavity. The sockets are advantageous because a faulty IC package can be replaced with an operable IC package without the need to unsolder the faulty IC package and solder an operable IC package. Therefore, the socket saves time and expense in replacing a faulty IC package.
Accordingly, it is the object of this invention to provide a means to dissipate heat from an IC package or other electrical component which meets the aforementioned requirements and solves the aforementioned problems.
Another object of this invention is to provide a means to dissipate heat from an IC package or other electrical component which is mounted in a socket.
An additional object of this invention is to provide a means to dissipate heat from an electrical component located in a socket whereby the invention can include cooling fins or the invention can transfer the heat to a heat sink.
A further object of this invention is to provide a means to dissipate heat from an electrical component which directs the thermal flow downward into the socket or socket cavity.
Another object of the invention is to provide an additional means to dissipate heat from an electrical component which primarily directs the thermal flow upward away from the socket or socket cavity.
Another object of this invention is to provide a means to dissipate heat from an IC package or electrical component which is inexpensive to manufacture, reliable in operation, and efficient in dissipating heat.
Other objects and advantages of the invention will become apparent upon reading the following detailed description and appended claims, and upon reference to the accompanying drawings.